Coded bit padding

ABSTRACT

A method is described for adding coded bit padding for a orthogonal frequency division multiplexing (OFDM) data transmission device.

BACKGROUND

Orthogonal frequency division multiplexing (OFDM) provides a useful wayto modulate data for transmission. OFDM may be considered a form ofdigital multi-carrier modulation. A number of orthogonal sub-carriersare used to carry data. Data for transmission is then divided intoseveral parallel data streams for transmission. Each of the sub-carriersmay in turn be modulated using binary phase-shift keying (BPSK),quadrature phase-shift keying (QPSK), quadrature amplitude modulation(QAM), and so forth.

An OFDM system uses several carriers, or “tones,” for functionsincluding data, pilot, guard, and direct component. Data tones are usedto transfer information between the transmitter and receiver via one ofthe channels. Pilot tones are used to maintain the channels, and mayprovide information about time/frequency and channel tracking. Guardtones may be inserted between symbols during transmission to avoidinter-symbol interference (ISI), such as might result from multi-pathdistortion. These guard tones also help the signal conform to a spectralmask. The nulling of the direct component or DC may be used to simplifydirect conversion receiver designs.

In certain instances, an OFDM system, in order to send out OFDM symbols,implements padding bits. Bit padding allows a full OFDM symbol to besent, although the padding bits per se are not needed. Bit paddingtypically may be implemented at the physical or PHY layer.

The Institute of Electrical and Electronics Engineers (IEEE) 802.11standard defines protocols for wireless transmission. As the IEEE 802.11standard evolves, support for new tone allocations, modulation andcoding can create issues and problems. In particular, a condition canarise, where the PHY layer bit padding used in legacy IEEE 802.11systems may not work.

BRIEF DESCRIPTION OF THE DRAWINGS

The detailed description is described with reference to accompanyingfigures. In the figures, the left-most digit(s) of a reference numberidentifies the figure in which the reference number first appears. Thesame numbers are used throughout the drawings to reference like featuresand components.

FIG. 1 is an illustrative system for implementing coded bit padding.

FIG. 2 is a block diagram of a exemplary device that implements codedbit padding.

FIG. 3 is a block diagram of an exemplary encoder module for bitpadding.

FIG. 4 is a flow chart for a process of coded bit padding.

DETAILED DESCRIPTION Overview

In order to implement legacy IEEE 802.11 coding and interleaving schemesand systems, coding schemes are implemented to move bit padding in thephysical or PHY layer from before coding (encoder) to after coding(encoder). Exemplary implementations include an encoder module indevices to provide for such schemes and processes.

Illustrative System

FIG. 1 is an illustrative system 100 that implements coded bit padding.The system 100 can include multiple devices 102 in communication withone another. In this example, the system includes a device 102(1) withan encoding module 104(1). Device 102(1) is coupled via a wiredconnection 106 to a device 102(2). Device 102(2) includes an encodingmodule 104(2). System 100 further includes a device 102(2) in wirelesscommunication 108 with device 102(N). Device 102(3) includes an encodermodule 104(3), and device 102(N) includes an encoder module 104(N).

Encoder modules 104 are implemented to provide coded bit padding forOFDM symbols transmitted by devices 102. In certain implementations, thedevices 102 may include OFDM modules (not shown) to generate an OFDMsignal.

Each device 102 can include a transmitter, receiver, or transceiver toconvey output (i.e., OFDM symbols). These transmitters, receivers, ortransceivers may be configured to convey the output via an electricalconductor, electromagnetic radiation, or both. Each device 102 includesone or more processors (described below) and a memory (described below)coupled to the processor(s).

Devices 102 can include wireless access points, radio frequencytransceivers, software defined radios, modems, interface cards, cellulartelephones, portable media players, desktop computers, laptops, tabletcomputers, net books, personal digital assistants, servers, standalonetransceiver interfaces, and so forth.

In exemplary operations, communication in system 100 can implement an 80MHz channel, or higher such as 120 MHz or 160 MHz and 256 QAM(quadrature amplitude modulation). In legacy IEEE 802.11, such featurescan be problematic for data tone selection. The encoding schemes andprocesses (i.e., encoding module 104) described herein, are directed tosuch issues.

The number of data tones implemented by system 100 may be even tonecounts of 216, 220, 222, 224, 228, 230, 232 and 234 for a 80 MHz system.These numbers are based on the reuse of the IEEE 802.11n interleaverstructure, and data bit flow. This is in addition to having a minimumtone count of at least two times the 40 MHz (i.e. 80 MHz) IEEE 802.11nsystem.

The described encoding schemes consider the addition of 256 QAM, withcode rates such as ⅔ and ⅚, where the number of data tone count optionsdrops by a half. This is due the numerology and flow used in the IEEE802.11a/n standard. A code rate of ⅔ is attractive when coupled with 256QAM. The ⅔ code rate is more effective from a transmitter poweramplifier perspective, than rates such as ¾ or ⅞, and can allow adecrease in power consumption or a less expensive device 102 to beutilized when implementing the same transmit range as legacy IEEE 802.11systems. Furthermore, if legacy 20 MHz IEEE 802.11 systems use 256 QAM,coding rates of ⅔ or ⅚ may not be used. This can be the case, becauseproviding new tone allocation (configurations) may not fit exactly in aninteger number of OFDM symbols, unlike legacy IEEE 802.11 systems thathave data tone counts and modulation and coding that create payloadsthat fit exactly in an integer number of OFDM symbols.

For legacy IEEE 802.11 encoding schemes, consideration can be made fortwo constraints, which depend on the OFDM symbol size and the encoder(encoding module 104). The first constraint is that the number of codedbits per OFDM symbol or Ncbps should be an integer. The secondconstraint is that the number of data bits per OFDM symbol or Ndbpsshould also be an integer. An integer for Ndbps can assure that all datalengths work with no additional padding using the current IEEE 801.11a/n equations. If Ndbps is not an integer, then many payload sizes canresult in a non-integer number of padding bits, or the number of encodedbits exceeding the number of OFDM symbols. In either case, this leads toa minimum of one additional OFDM symbol that is not needed, whichincludes only padding bits. Current IEEE 802.11a/n equations requirethat Ncbps and Ndbps be integers. In certain cases, the IEEE 802.11a/nequations the padding bits to be added can be a non integer, whichresults in the inability to fill out the packet.

The schemes processes described herein are not limited to by the havingNcbps and Ndbps to be integers. The schemes and processes that aredescribed provide that for data tone counts to be used with variousmodulation or coding scenarios, to move the bit padding operation fromthe input of the encoder (coding), to the output of the encoder(coding), after the bits have been encoded. The following equation (1)can be used to compute the number of padding bits to fill out the leastnumber of OFDM symbols to transmit the media access control or MACpayload.

N _(Pad) =N _(SYM) *N _(SD)−(N _(MACBYTES)*8+16+6)  (1)

Where N_(Pad) is the number of padded symbols to be added; N_(SYM) isthe number of OFDM symbols based on the equation in IEEE 802.11a/nstandard; N_(SYM) is the number of data tones; N_(MACBYTES) is thenumber of MAC layer bytes that are being passed to the PHY layer; 16 isthe length of the service field; and 6 is the length of the tail bits.

This bit padding approach can remove an IEEE 802.11 requirement on theNdbps and Ncbps for data tone allocation, with a number of modulationand coding combinations. The bit padding approach is also intended to bebackwards compatibility with IEEE 802.11 systems/standards incorporatedinto current and legacy IEEE 802.11 processing chains. Furthermore, sucha bit padding approach can allow for various combinations of data tones,modulation, and coding without restricting one of the aforementionedvariables. In particular, restricting the number of data tones can lowersystem data rate, as would disallowing 256 QAM. Restricting the codingcan, as discussed above, potentially increase cost or power consumption.In prior or legacy IEEE 802.11 systems, the numerology can only allowfor integer data bits per OFDM symbol and integer number of coded bitsper OFDM symbol. A new signal field can be required for next generationIEEE 802.11 systems, where knowledge of the padding method and numbermay have to be known. The bit padding approach can provide modulationand coding rates used in bandwidths of 60 to 160 MHz, and in particular80 MHz.

Device Architecture

FIG. 2 illustrates an exemplary device 104 that implements coded bitpadding. The device 104 includes devices 104(1), 104(2), 104(3) and104(N). Device 104 describes certain components and it is to beunderstood that described components can be replaced with othercomponents, and combined with one another. Additional components anddevices may also be included in device 104.

A host microprocessor or processor 200, which can include multipleprocessors, is provided. The processor 200 can be connected or coupledto a memory 202. Memory 202 can include multiple memory components anddevices. The memory component 202 can be coupled to the processor 200 tosupport and/or implement the execution of programs, such as keygeneration and delivery protocol. The memory component 202 includesremovable/non-removable and volatile/non-volatile device storage mediawith computer-readable instructions, which are not limited to magnetictape cassettes, flash memory cards, digital versatile disks, and thelike. The memory 202 can store processes that perform the methods thatare described herein.

In an implementation, the IEEE 802.11 standard is extended andimplemented by device 104. Therefore, in such an implementation, device104 includes particular hardware/firmware/software configurations tosupport the IEEE 802.11 standard. Device 104 implements a common mediumaccess control or MAC layer, which provides a variety of functions thatsupport the operation of IEEE 802.11 based wireless communications. Asknown by those skilled in the art, the MAC Layer manages and maintainscommunications between IEEE 802.11 wireless communication devices bycoordinating access to a shared radio channel and utilizing protocolsthat enhance communications over a wireless medium. The MAC layer usesan 802.11 physical or PHY layer, to perform the tasks of carriersensing, transmission, and receiving of OFDM symbols.

The device 104 further includes encoder module 104. The encoder module104, which is further described below, is used to perform receiving databits, encoding (coding), modulating, and outputting OFDM symbols.Furthermore, one or more antennae 206(1) to 206(N) can be included withor connected to the device 104. Antennae 206 can include multipleantennae for multiple input, multiple output (MIMO) operation. Antenna210 can be configured to receive and send transmission.

Encoder Module Architecture

FIG. 3 illustrates an exemplary encoder module 104 for bit padding. Theparticular operating parameters described are illustrative and are notintended to be limiting. It is to be understood that other operatingparameters may be implemented.

In this example, encoder module 104 can operate using an 80 MHztransmission bandwidth with 224 data tones, implementing 256 QAM with acode rate of ⅔. The data bits 300, include 200 bytes (200*8) or 1600data bits, which are passed from the MAC layer. The data bits 300 arepassed onto a payload represented by a service field 302 having 16 bits,the data bits 304 (1600 data bits), and tail bits 306. The tail bits 306are used to flush the encoder module 104. The payload is sent to ascrambling process 308 and encoded 310 at a ⅔ rate. The scramble 308 andencode 310 can be presented as a coding or encoding module 312. Additionof padding bits represented by module 314, is performed. In thisexample, 1151 symbols or bits are added. Interleaving and modulationmapping can be performed as shown in module 316. An output buffer 318receives the interleaved and modulated symbols which included 3584 codedsymbols or 450 modulation signals.

A minimal number of OFDM symbols represented by OFDM Symbol 1 320 andOFDM Symbol 2 322 is shown. The OFDM Symbol 1 320 and OFDM Symbol 2 areoutput of the output buffer 318. In contrast to schemes that implementthe use of padding bits prior to coding or encoding (i.e., encoding312), no extra padding bits are needed, and no extra OFDM symbol isgenerated.

Exemplary Process for Coded Bit Padding

FIG. 4 is a flow chart for an example process 400 for coded bit padding.As an example, the code bit padding may be performed using the encodermodule 104 of the device 102. The order in which the method is describedis not intended to be construed as a limitation, and any number of thedescribed method blocks can be combined to implement the method, oralternate method. Additionally, individual blocks can be deleted fromthe method without departing from the spirit and scope of the subjectmatter described herein. Furthermore, the method can be implemented inany suitable hardware, software, firmware, or a combination thereof,without departing from the scope of the invention.

At block 402, receiving a data payload for OFDM transmission isperformed. As discussed above, the data payload can be passed from theMAC layer to the PHY layer. The received payload can include data bitsalong with service data bits and tail bits. The data payload may bedetermined by a number of data tones, which as discussed above, can bean even number tone count.

At block 404, coding or encoding is performed on the data payload. Asdiscussed above, 256 QAM may be implemented, and code rates such ⅔ or ⅚.Furthermore, bandwidth operation can include 60 to 160 MHz, andparticularly 80 MHz.

At block 406, adding padding bits is performed. The number of paddingbits may be derived by the following equation as discussed above, tofill out the least number of OFDM symbols to transmit the media accesscontrol or MAC payload.

N _(Pad) =N _(SYM) *N _(SD)−(N _(MACBYTES)*8+16+6)  (1)

Where N_(Pad) is the number of padded symbols to be added; N_(SYM) isthe number of OFDM symbols based on the equation in IEEE 802.11a/nstandard; N_(SYM) is the number of data tones; N_(MACBYTES) is thenumber of MAC layer bytes that are being passed to the PHY layer; 16 isthe length of the service field; and 6 is the length of the tail bits.In addition, interleaving and modulation may occur after padding bitsare added.

At block 408, outputting a minimal number of OFDM symbols is performed.The number of coded bits per OFDM signal or Ncbps can be an integer.Also, the number of data bits per OFDM signal or Ndbps can also be aninteger.

CONCLUSION

Although specific details of illustrative methods are described withregard to the figures and other flow diagrams presented herein, itshould be understood that certain acts shown in the figures need not beperformed in the order described, and may be modified, and/or may beomitted entirely, depending on the circumstances. As described in thisapplication, modules and engines may be implemented using software,hardware, firmware, or a combination of these. Moreover, the acts andmethods described may be implemented by a computer, processor or othercomputing device based on instructions stored on memory, the memorycomprising one or more computer-readable storage media (CRSM).

The CRSM may be any available physical media accessible by a computingdevice to implement the instructions stored thereon. CRSM may include,but is not limited to, random access memory (RAM), read-only memory(ROM), electrically erasable programmable read-only memory (EEPROM),flash memory or other solid-state memory technology, compact diskread-only memory (CD-ROM), digital versatile disks (DVD) or otheroptical disk storage, magnetic disk storage or other magnetic storagedevices, or any other medium which can be used to store the desiredinformation and which can be accessed by a computing device.

1. A method implemented by a device for bit padding, for orthogonalfrequency division multiplexing (OFDM) transmission, comprising:receiving a data payload for the OFDM transmission; encoding the datapayload; adding the bit padding to the encoded data payload; andoutputting a minimal number of OFDM symbols.
 2. The method of claim 1,wherein the receiving provides for the data payload to be passed from amedia access control (MAC) layer to a physical (PHY) layer of thedevice.
 3. The method of claim 1, wherein the encoding is based on a ⅔rate.
 4. The method of claim 1, wherein the encoding implements 256quadrature amplitude modulation.
 5. The method of claim 1, wherein theadding the bit padding is defined by the equationN _(Pad) =N _(SYM) *N _(SD)−(N _(MACBYTES)*8+16+6)
 6. The method ofclaim 1, wherein the outputting the minimal number of OFDM symbols is oris not dependent on a number of coded bits per OFDM signal (Ncpbs) and anumber of data bits per OFDM signal (Ndps) to be an integer.
 7. Themethod of claim 1 further comprising interleaving and modulating afterthe adding of the bit padding to the encoded data payload.
 8. One ormore computer-readable storage media storing instructions that, whenexecuted by one or more processors, cause the one or more processors toperform acts comprising: processing a data payload that includes databits for OFDM transmission; encoding the data payload based onparticular data tones; adding bit padding to an encoded data payloadafter the encoding; and transmitting OFDM symbols representing a bitpadded encoded data payload.
 9. The one or more readable media of claim8, wherein the processing data payload includes service field bits andtail bits.
 10. The one or more readable media of claim 8, wherein theprocessing data payload is performed at a device's physical (PHY) layer.11. The one or more readable media of claim 8, wherein the encoding isimplemented for 80 MHz bandwidth transmission.
 12. The one or morereadable media of claim 8, wherein the adding bits is dependent on anumber of data tones.
 13. The one or more readable media of claim 8,wherein the transmitting is of a minimal number of OFDM symbols.
 14. Theone or more readable media of claim 8 further comprising interleavingand modulating after the adding bit padding the encoded data payload.15. A device for adding data bits for orthogonal frequency divisionmultiplexing (OFDM) transmission, comprising: one or more processors; amemory coupled to the one or more processors; and an encoder moduleconfigure to: receive a data payload; encode the data payload andgenerate an encoded data payload; add padding bits to the encoded datapayload; output a minimal number of OFDM symbols.
 16. The device ofclaim 15, wherein the encoder module encodes at a ⅔ rate.
 17. The deviceof claim 15, wherein the encoder module implements 256 QAM.
 18. Thedevice of claim 15, wherein the encoder module operates with 224 datatones.
 19. The device of claim 15, wherein the encoder module includes acoding module to perform the encode the data payload and generate theencoded data payload based on a particular data rate.
 20. The device ofclaim 15, wherein the encoder modules includes an interleaver thatinterleaves the encoded data payload after the padding bits are added.